Generally, in a rotary machine such as a gas turbine or a steam turbine, an annular gap is formed between a stationary member such as a stator blade and a member that rotates such as a rotating shaft. A working fluid passing through this annular gap ends up leaking from the high-pressure side to the low-pressure side. In order to prevent this, a shaft seal device is used. As one such shaft seal device, a conventional non-contact type labyrinth seal has been widely used. However, with this type of shaft seal mechanism, it is necessary to ensure that the fin distal end does not make contact with the surrounding members due to a shaft oscillation in a rotation transitional period or a thermal deformation due to a thermal transitional thermal deformation. For that reason, it is necessary to enlarge to some extent the space at the fin distal end, that is, the seal clearance, and thereby the leakage amount of the working fluid is increased.
As a technique for reducing the leakage amount of a working fluid in this kind of shaft seal mechanism, there is known a shaft seal that has a structure in which a thin plate having a predetermined width dimension in the axial direction of the rotating shaft is arranged in multiple layers in the circumferential direction of the rotating shaft (for example, refer to Patent Document 1). FIG. 9 shows an example of the configuration of this shaft seal. FIG. 9 is a perspective view that shows the configuration of the shaft seal.
This shaft seal 100 has a housing 102 that is arranged so as to surround the rotating shaft 101 at the outer periphery of the rotating shaft 101, and thin plates 105 that are fitted to the housing 102 and provided in a predetermined arrangement having a ring shape in the circumferential direction of the rotating shaft 101. In this shaft seal 100, as a result of the thin plates 105 sealing the outer periphery of the rotating shaft 101, the space surrounding the rotating shaft 101 is partitioned into a high-pressure side region and a low-pressure side region with the thin plates 105 serving as a boundary. A high-pressure side plate (side leaf) 104 is provided on the high-pressure side of the thin plates 105, and a low-pressure side plate (back leaf) 103 is provided on the low-pressure side of the thin plate 105. The high-pressure side plate 104 and the low-pressure side plate 103 are mounted on the housing 102 as guide plates that support the thin plates 105.
In this kind of shaft seal 100, although the distal ends of the thin plates 105 come into contact with the rotating shaft 101 with a predetermined pre-load when the rotating shaft 101 is stopped, since a lift force acts on the thin plates 105 due to the hydrodynamic effect when the rotating shaft 101 rotates, the distal ends of the thin plates 105 float up from the rotating shaft 101. Thereby, the thin plates 105 and the rotating shaft 101 enter a contactless state during rotation of the rotating shaft 101, and so prevention of wear between each thin plate and the rotating shaft is achieved.